This work will examine the factors which govern the rates of transition between equilibrium states of an allosteric protein. It will determine if the factors which are signifiant in determining the free energy of the equilibrium states are equally significant in determining the rates of transition between those states. Hemoglobin has been selected as a model allosteric protein because it has already been extensively described in structural and thermodynamic terms. In the course of this investigation the allosteric description of the equilibrium behavior of hemoglobin will also be further refined. The forward and reverse rates of transition between the T and R conformations of hemoglobin are to be measured. These rates will be determined by the use of modulated excitation spectroscopy, primarily studying hemoglobin with three ligands bound. Conformational change will be monitored by optical probes sensitive to the environment of the heme and of the subunit interfaces, as well as to the inter-subunit spacing. Measurements will be performed as a function of pH and temperature, on carboxyhemoglobin and oxyhemoglobin. Such measurements will also be performed for singly-ligated hemoglobin, for deutero-heme substituted hemoglobin, and for iron-cobalt hybrids.